Diesel Engine FundamentalsDOE-HDBK-1018/1-93DIESEL ENGINESBrake horsepowerrefers to the amount of usable power delivered by the engine to thecrankshaft. Indicated horsepower can be as much as 15% higher than brake horsepower.The difference is due to internal engine friction, combustion inefficiencies, and parasiticlosses, for example, oil pump, blower, water pump, etc.The ratio of an engine's brake horsepower and its indicated horsepower is called themechanical efficiencyof the engine. The mechanical efficiency of a four-cycle diesel isabout 82 to 90 percent. This is slightly lower than the efficiency of the two-cycle dieselengine. The lower mechanical efficiency is due to the additional friction losses and powerneeded to drive the piston through the extra 2 strokes. Engines are rated not only in horsepower but also by the torque they produce. Torqueis a measure of the engine's ability to apply the power it is generating. Torque iscommonly given in units of lb-ft.Rev. 0ME-01Page 19
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business